The invention relates to a self-closing cover element which, preferably in the region of one end, is pivotable, about an at least virtually horizontal pivot pin, between a covering position and a release position, it being possible for the cover element to pivot back from the release position to the covering position after a certain time of its own accord. WO-95/08.9^1 has disclosed an automatic closure mechanism which is intended to move automatically a toilet seat and lid back from an open position into a closed position after a period of time. Use is made in this mechanism of a damping spring mechanism which comes into action after a short period of time. Using a damping spring mechanism of this kind to realize a cover element which closes automatically, i.e. is self- closing, after a certain time is relatively expensive and moreover under many circumstances cannot be achieved effectively. Possible examples here are relatively small and/or relatively cheap products.

An object of the present invention is to provide a relatively simple self-closing cover element which can preferably be produced at relatively low cost and which, moreover, only closes after a certain period of time, which period can preferably be influenced, for example can be influenced by making certain design selections. A further object of the invention is to provide a self-closing cover element which has a high level of operational reliability and can be produced with small dimensions and low structural weight. A further object is to provide a self-closing cover element which has a wide variety of possible applications.

The abovementioned objects of the invention are achieved by providing a self-closing cover element which, preferably in the region of one end, is pivotable, about an at least virtually horizontal pivot pin, between a covering position and a release position, it being possible for the cover element to pivot back from the release position to the covering position after a certain time of its own accord, characterized in that the cover element comprises at least one guide track which crosses the pivot pin and which preferably extends in a direction essentially transverse to that of the pivot pin, in that a body is arranged in the guide track, which body, under the effect of its own weight, can move in

the guide track from an upper end, which in the release position is situated at a higher level, of the guide track to a lower end, situated at a lower level, of the guide track, the cover element and the body together having a movable, instantaneous centre of gravity with an instantaneous line of gravity, and, in the release position, the upper end and lower end, viewed in the horizontal direction, lying on either side of the pivot pin, such that when the instantaneous line of gravity passes or has passed the pivot pin as a result of the movement of the body, a closure movement of the cover element is brought about in order for it to pivot back from the release position to the covering position. As will be clear, a self-closing cover element of this kind can easily be realized by designing the cover element to be pivotable with regard to a pivot pin and by providing it with a guide track which crosses the pivot pin and which is provided with a body which can move through it. A body of this kind may be a ball or a cylinder, but may also be a block which is able to perform a translational movement through the guide track. Furthermore, the body may be either a viscous or solid body. The important factor is that the body be able to move through the guide track and that it moves under the effect of movement of the instantaneous centre of gravity, which is defined by the cover element (including the guide track) and the body, in order, given sufficient movement (when the instantaneous line of gravity, i.e. the vertical through the instantaneous centre of gravity, passes or has passed the pivot pin), to bring about a closure movement of the cover element by reversing the turning moment acting on the pivot pin.

Crossing of the pivot pin and guide track is understood here to mean that the pivot pin and the guide track may optionally intersect one another (in which case the pivot pin, or at least the axis of rotation thereof, extends through the guide track) but equally they may have no common intersection point (in which case the pivot pin and the guide track cross one another at a distance apart) .

In order to allow the self-closing cover element according to the invention, which in relative terms is very simple, to be able to act repeatedly, it is advantageous according to the invention if, in the covering position, the so-called upper end of the guide track is situated at a lower level than the so-called lower end of the guide track. (The definitions of upper end and lower end here relate to the open, or so- called release, position). This measure makes it possible for the body,

when the cover element is situated in the covering position, to move back automatically towards the so-called upper end, in order then to be back in the starting position after the self-closing cover element is opened or moved into the release position again, so as to operate the self- closing mechanism.

In order to ensure a reliable self-closing action of the cover element according to the invention, it is advantageous if, in the release position, the guide track crosses above the pivot pin, that is to say at a distance from the latter. The reliable self-closure of the cover element is improved still further if the pivot pin, in the covering position, crosses below the guide track, that is to say at a distance from the latter. This has the advantage that, in the covering position, the body, owing to its position, improves the closure, that is to say the ability of the cover element to adopt and maintain a covering position. The time interval after which the self-closing cover element closes, that is to say the passage of time after which the cover element pivots back, of its own accord, from the release position into the covering position (for short, also referred to here as time delay) can be realized according to the invention in a relatively simple manner by providing a curved course of the guide track, i.e. making the latter curved in its longitudinal direction, the guide direction.

In order to ensure that the self-closing cover element continues to operate even over a relatively long period of time, it is advantageous according to the invention if the guide track is sealed in an essentially fluid-tight manner, so that it is impossible for contamination to penetrate into the guide track, which contamination could hinder the movement of the body through the guide track. Moreover, the so-called time delay can advantageously be set by filling the guide track with a suitable fluid, such as a gas, a gas mixture, a liquid, a liquid mixture or a gas/liquid mixture. If the guide track is filled, for example, with water, the body will move more slowly through the guide track than if this guide track is filled with air. The so-called time delay can thus be set as desired by suitable selection of a fluid or fluid mixture. Reliable operation can furthermore be ensured according to the invention if the body, which can move through the guide track under the influence of its own weight, is a body of revolution, that is to say a body which is able to roll. A body of this kind will not easily become

stuck in the guide track. However, it is also very conceivable according to the invention, and under certain circumstances even very advantageous, if the body which can move through the guide track is able to move with a translational sliding motion, or possibly with a combination of translational sliding motion and a rolling motion.

According to a further advantageous embodiment of the invention, the at least one guide track comprises a closed channel and the body which can move therein is a liquid or liquid mixture, the viscosity of the liquid or the liquid mixture and the cross-section of the channel preferably being such that the liquid or liquid mixture, at least in the region of the upper end, moves as a whole, as a column, through the guide track. The channel is in this case preferably of transparent or at least partially transparent design. This makes it possible to detect visually where the liquid or the liquid mixture is situated. In an embodiment of this kind, an obstruction element may, for example, be arranged in the channel in the vicinity of the so-called upper end, which obstruction element allows the relatively unimpeded passage of the liquid or the liquid mixture in the direction of the upper end but delays the passage of the liquid or the liquid mixture in the opposite direction, i.e. in the direction from the upper end to the lower end, for example allows it through in drops. If the cover element is then situated in the release position, the liquid or the liquid mixture will initially be situated entirely at the upper end of the obstruction element and will then move past the obstruction element, for example drop by drop, to the lower end, so that the cover element, when a sufficiently large quantity of liquid or liquid mixture has passed the obstruction element in the direction of the lower end, commences the closure movement, after which the liquid allowed to pass by the obstruction element in the direction of the lower end can flow back again, essentially with little hindrance, to the top-end side of the obstruction element. The obstruction element may in this case comprise, for example, two so-called non-return valves which each allow passage in opposite directions. One non-return valve will then allow passage in the direction of the upper end, the liquid or the liquid mixture then being subject to relatively little resistance from this non-return valve. The other non¬ return valve will then allow liquid or liquid mixtures to pass through relatively slowly in the direction of the lower end, which slow passage may, for example, be drop-by-drop. It is also conceivable to design the

channel such that its cross-section increases in the direction from the upper end to the lower end, optionally gradually or optionally widening at certain points along the length of the channel. Both embodiments, that is to say the changes in cross-section and the restriction element, allow the liquid or the liquid mixture in the covering state to collect relatively quickly in the vicinity of the so-called upper end in order, in the release position, only to close the cover element again after a certain time delay. The self-closing cover element can thus quickly be ready for use again (reopening) after it has closed. However, the design may also be kept simpler by providing a channel with an essentially constant cross-section, in which case, however, it will be advantageous if the liquid or the liquid mixture is to move through this channel essentially as a single column.

A self-closing cover element of this kind in which the guide track is a channel and in which the body is a liquid or liquid mixture may advantageously comprise a number of these channels each containing a liquid or liquid mixture, the channels running parallel to one another and being situated adjacent to one another. The entire cover element may thus optionally be composed of a multiplicity of channels of this kind containing a liquid or liquid mixture.

In order to be able to adjust the time delay before a closure motion of the self-closing cover element starts and simultaneously to ensure that the cover element is quickly ready to be opened once more after having been closed, while retaining a satisfactory action of the self-closing mechanism, it is advantageous according to the invention if the guide track is provided with delay means which, when the body moves past them under the influence of its own weight, allow it to pass by them in an impeded manner, and, viewed in the release position: the delay means are situated in that section of the guide track which is situated at a higher level, preferably at the upper end thereof; and after passing the delay means, the body proceeds towards the lower end of the guide track in an essentially umimpeded, or at least less impeded, manner. By allowing the body to move further towards the lower end in an essentially unpeded manner after a certain time delay it is possible to achieve a certain impulse impact or collision impact on reaching the

lower end, which impulse assists the reliable closure of the cover element.

In an embodiment of this kind with delay means, it is advantageous according to the invention if the delay means, viewed in the covering position, are arranged on the top side of the guide track at a distance above the base of the guide track which is such that the body can pass essentially unhindered below the delay means to the upper end. If the self-closing cover element is then situated in the release position, the body will have to pass along the delay means, since in this position of the self-closing cover element the delay means are situated on the bottom of the guide track, while when the self-closing cover element is situated in the covering position these delay means are situated at the top of the guide track, so that the body can pass essentially unimpeded below these delay means and can thus move quickly back to the so-called upper end under the force of gravity, in which position the self-closing cover element is again ready to be reopened with a following reliable action of the self-closing mechanism.

It will be clear that the sufficient distance of the delay means from the base can be achieved, for example, by physically separating the guide track into a top track and a bottom track at the location of the delay means.

In order to make the self-closing cover element foolproof, it is advantageous according to the invention if the delay means, viewed in the covering position, are open towards the base of the guide track in such a manner that, in the covering position of the cover element, the body can fall out of the delay means. This ensures that if the self- closing cover element is closed prematurely for whatever reason, for example owing to a manual manipulation by a person, without the delay mechanism having been able to exert its full effect, the body can release itself from the delay means and move back to the starting position, i.e. the so-called upper end.

In order in an embodiment of this kind to ensure that the body is directed towards the delay means during the move from the covering position to the release position, it is advantageous according to the invention if viewed in the covering position, one-way passage means are provided between the upper end of the guide track and the delay means, which passage means only allow the body to pass in the direction towards the upper end, and if directional means are provided which, viewed in the

release position, direct the body towards the delay means. One-way passage means and directional means of this kind can be realized in a variety of ways, as will be clear to an average person skilled in the art. According to an advantageous embodiment of the invention, the one- way passage means and the directional means together comprise a resilient lip, which extends upwards from the base of the guide track, preferably obliquely upwards in the direction of the upper end.

According to the invention, the delay means may be provided in a variety of ways. According to an advantageous embodiment, the delay means comprise friction means which are arranged along the guide track and with which the body will then come into contact, which friction means have a relatively great coefficient of friction, at least compared to the remainder of the guide track.

In an embodiment with friction means, the body will be a body which is able to roll, and the friction means will be arranged or designed such that the body makes contact with the friction means at two points or in two regions, which are preferably situated on opposite sides of the axis of rotation of the body, where it will be subject to a different frictional resistance. This prevents the body from remaining stuck between the friction means.

According to an advantageous embodiment, the friction means may be realized in a simple manner in the form of strips which are arranged on either side of the guide track and have a relatively great frictional resistance which is preferably not the same on both sides. In an embodiment with delay means, according to the invention the time delay between pivoting into the release position and pivoting back into the covering position can be selected by suitably dimensioning the delay means, optionally combined with suitably dimensioning the guide track and the body which can move through it. Dimensioning is to be understood here to mean choosing the dimensions and choosing the material and/or the material properties.

In the event that friction means with uneven frictional resistance are used, it is possible according to the invention to use friction means made of, inter alia, the following materials or combinations thereof: the friction means providing a relatively greater frictional resistance may comprise a hard but slightly resilient material, such as for example hard rubber or a thermoplastic elastomer, and the friction

means providing a relatively lower frictional resistance may then comprise a softer compressible material; the friction means providing a relatively greater frictional resistance may comprise a foamed plastic material with a closed cell structure; the friction means providing a relatively lower frictional resistance may comprise a foamed plastic material with an open cell structure.

According to an advantageous embodiment of the invention, the guide track may, in the release position, extend at a steep angle of, for example, at least 60° , preferably at least 75°. to the horizontal. The body can then move relatively easily along the guide track and, in the event of so-called delay means being used, the body can fall more or less freely after passing the so-called delay means, thus bringing about a relatively great impulse or collision impact when the body strikes the so-called lower end of the guide track. In order to ensure that the body returns or moves back to the so-called upper end efficiently and quickly in the covering position, in practice it has proven sufficient for the guide track, in the covering position, to extend at an angle of at least about 3 to 5 degrees to the horizontal, the so-called upper end then being situated at a lower level than the so-called lower end.

The invention furthermore relates to a storage system, such as a container, intended to accommodate materials and objects, comprising a cover in the form of a self-closing cover element according to the invention. Such a storage system according to the invention may, for example, accommodate one or more removable interior boxes. Interior boxes are here understood in particular to mean sub-containers which can be arranged in a larger container, which larger container can be closed off by means of the self-closing cover element according to the invention and can be opened. Interior boxes of this kind may according to the invention have recesses on one side, which recesses are intended for accommodating materials or objects in a grouped and separate manner. The storage system according to the invention may moreover also comprise a linkage of larger containers with one or more interior boxes in each of the larger containers.

The invention furthermore also relates in particular to the use of a container provided with a self-closing cover element according to the invention, for products, goods or objects which have to be easily

accessible but hygienically stored, such as for example implements required for dental or medical treatment, foodstuffs and confectionery goods.

The invention will be explained in more detail in the following text with reference to exemplary embodiments which are depicted in the drawing and are only intended as examples and not to limit the invention. In the drawings:

Figure 1 shows a diagrammatic, perspective view of a storage system according to the invention which is in the closed position and is provided with a self-closing cover according to the invention;

Figure 2 shows a view in accordance with Figure 1, but with the self-closing cover in the open position;

Figure 3 shows a very diagrammatic side view of a self-closing cover element according to the invention in the open position; Figure k shows a very diagrammatic view corresponding to that of Figure 3, except that Figure 4 shows the position in which the cover element has just moved into its closed position;

Figure 5 shows a diagrammatic and perspective view of a further exemplary embodiment of a storage system according to the invention, with the self-closing cover having been omitted;

Figure 6 shows a diagrammatic and perspective view of yet another embodiment of the storage system according to the invention, with the self-closing cover having been omitted;

Figure 7 shows a diagrammatic, perspective view of yet another embodiment of a storage system according to the invention, with the self- closing cover having been omitted.

Figure 8 shows a diagrammatic and perspective view of yet another embodiment according to the invention, with the self-closing cover having been omitted; Figure 9 shows a diagrammatic and perspective view, partially in section, of yet another embodiment of a container according to the invention, in the closed position;

Figure 10 shows a view corresponding to that of Figure 9, but in the open position; Figure 11 shows a very diagrammatic, perspective view of a container according to the invention, with the self-closing cover depicted in the closed position;

Figure 12 shows a very diagrammatic cross-sectional view of the container in accordance with Figure 11, in the open position and in accordance with the arrow XII-XII in Figure 11.

Figure 13 shows a view corresponding to that of Figure 12, but in the closed position.

The storage system 1 shown in Figure 1, which in the following text may be regarded as a storage system which is used by the dentist in a dental practice in order to store fragile and sterilized materials and objects therein which are used to treat patients, comprises a casing 5 with a self-closing cover on its top side, this cover being pivotable about a virtually horizontal pivot pin or pivot axis 3- On its top side, the cover 2 comprises a guide track 4 which is located parallel to the longitudinal axis of the cover 2. A body 6 which can move under the influence of its own weight is positioned inside the guide track 4. At the front side 7 facing the user, the cover 2 comprises a handle 8, by means of which the cover 2 can be moved into an open position (depicted in Figure 2) in accordance with the wishes of the user. As can be seen from Figure 1, the guide track in this case runs transversely to the pivot pin, although the guide track can also run at an angle other than 90° to the pivot pin.

Figure 2 shows the storage system 1 with the self-closing cover 2 in a completely open position. As a result, the internal part of the casing 5. with an interior box 9 accommodated therein, becomes visible. Recesses 10 are made at the top of the interior box 9, in which recesses, for example, UV-sensitive materials can be accommodated and protected from light with the cover 2 closed. Furthermore, a hollow holding space 11 in which, for example, sterilized cotton buds can be accommodated, is arranged in the same interior box 9. at the front side 7 facing towards the user. In addition, a coupling element 12 is arranged on the underside of the casing 5. which coupling element is partially accommodated inside a slot space 13 shown in Figure 1 and serves to couple a plurality of storage systems 1 together. Due to the fact that the coupling element 12 can be used to couple together a plurality of storage systems, the user is in a position to create an orderly and stable modular storage system, in which the coupling element 12, owing to its own weight, can also serve as a counterweight to enhance the stability against tipping over.

Figures 3 ^an ^ ^ very diagrammatically show how the self-closing cover element 20 according to the invention works. This cover element 20 may, for example, be used as a cover for a container, for example the storage system from Figure 1. Figure 3 diagrammatically shows a guide track 24 which is located in the cover element 20. The closed position of the cover element 20 is depicted in Figure 3 by means of a dashed contour line of the guide track 24. In this closed position, the body 26 which can move through the guide track 24 is situated on the front side 27, facing towards the user, of the cover element. If the user moves the cover element 20 as indicated by arrow A to a release position, or open position, depicted by means of an unbroken contour line, the body 26 is situated in a position in which the potential energy of the body 26 has increased by comparison with its previous position in the covering, or closed, position of the cover element 20.

After reaching this position, the body 26, under the influence of the force of gravity, will move along the guide track 24 to positions of lower potential energy. The movement of the body 26 can be attenuated by a viscous liquid accommodated within the guide track 24, as a result of which the body runs along the guide track at an essentially constant speed. However, the movement can also be delayed in other manners, as will become clear below.

During this movement, the common centre of gravity, which is formed by the body 26 and the cover element 20, is situated at such a position that the force of gravity directed along a line through this centre of gravity (that is to say along the line of gravity) exerts a moment with regard to the pivot pin 23, which moment for the time being holds the cover 2 in an open position.

After a time interval, which in this case can be set, inter alia, by selecting a suitable viscous liquid, has passed, the body 26 has moved under the influence of the force of gravity to a position of still lower potential energy, the common centre of gravity of cover element 20 and body 26 having adopted a position which is such that the force of gravity, directed along a line through this common centre of gravity, exerts a moment about the pivot pin 23, such that the cover element 20 executes a closing movement, as indicated by the arrow B shown in Figure 4, to a closing position.

The closed or closing position of the .-over 20 shown in Figure 4 is depicted by means of an unbroken contour line. In this position of the cover element 20, the body 26 is situated at a position within the guide track 24 which is remote from the user. From this position, the body 26 still has some potential energy, as a result of which it moves within the guide track 24, under the influence of it own weight, to a position which is situated at the front side 27, facing towards the user, of the cover. The body 26 is then ultimately situated in its original starting position and the cover element can be opened again, after which the self-closure mechanism can again come into action. In this way, it has thus proved possible to provide a self- closing cover which after an interval of time moves from a position allowing access to a container to a position which closes the container, without the intervention of the user. Furthermore, the form of the guide track 24 is not important for the action of a self-closing cover element 20 of this kind. Tests have shown that a slightly curved guide track does not impede the self- closure action and may provide an advantage in terms of controlling the self-closure mechanism. It has also been found that the peripheral shape of the body 26 is also not bound up with a preferred shape. However, it has been found that if the body 26 is a body of revolution which performs a rolling motion within the guide track 24 it is possible to achieve an advantageous, favourable action by comparison with a body which performs a translational sliding motion within the guide track. In addition, the type of medium which fills the guide track 4 is not really important for the self-closure action of the cover 20. It has been found that a gaseous medium within the guide track 4 exerts a reduced attenuating or inhibiting action on the body 6, with the result that the time interval before a closing movement from an open position to a closed position of the cover 2 is carried out has been found to be very short.

A viscous liquid accommodated within the guide track 4 provides a longer desired span of the time interval, within which time interval, for example, the dentist can pick up the materials or objects required to treat patients out of the storage system. As soon as the dentist has taken a material or object out of the storage system, he can immediately turn his attention to further activities without worrying about closing the cover.

As will be clear from Figures 3 and 4, the guide track, at least in the open or release position of the cover element 20, extends on either side of a vertical or perpendicular line 21 through the rotation pin or axis of rotation 23- When the body 26, starting from the position depicted by unbroken lines in Figure 3, has moved sufficiently far past the perpendicular line 21, the instantaneous centre of gravity defined by the cover element 20 and body 26 together, in particular the line of gravity running vertically through this centre of gravity, will also move past the perpendicular line 21, from which moment the movement indicated by arrow B in Figure 4 is commenced. As will be clear from Figures 3 and 4, the curved form of the guide track 24 depicted in those figures has an advantageous effect, in that the body 26, during the movement indicated by arrow A, is prevented from starting to move downwards along the guide track 24 prematurely, or at least too prematurely. Furthermore, it will be clear from Figure 3 that the guide track 24 in the release or open position crosses above the axis of rotation or pivot pin 23. In the position depicted in Figure 4, or at least the position indicated in unbroken lines, the guide track 24 crosses below the pivot pin or axis of rotation 23. It is clear from Figures 3 arid 4 that this crossing takes place at a distance apart.

Figures 5 to 8 show a plurality of possible embodiments of interior boxes 9, which have proven useful for storing materials and objects which the dentist considers important in an orderly and conveniently arranged manner, but also hygienically. Since these embodiments are largely similar to those of Figures 1 and 2, the same reference symbols are used for corresponding parts.

Thus, for example, Figure 5 shows an interior box 9 with recesses 10 made in the top for accommodating fragile materials such as sealants and bondings. Furthermore, a hollow space 11 is provided at the front of the interior box 9. for accommodating cotton buds 14.

Figure 6 shows a storage system with divided interior boxes 9 in which small recesses 15 are made at the top for holding sets of drill bits 16.

Furthermore, Figure 7 shows a following embodiment of an interior box for holding rolls of cotton wool 17, and Figure 8 shows an embodiment of an interior box 6 for holding wedges 18.

As will be clear from Figures 5 to 8, the self-closing cover has been omitted in all these figures, only its axis of rotation being

shown. The self-closing cover from Figures 1 and 2 can readily be used in these embodiments as the self-closing cover, as will be clear.

Figures 9 and 10 show a further exemplary embodiment of a self- closing cover element 31 according to the invention, used with a box 30. Viewed from the top, the box 30 is essentially rectangular with longitudinal walls 3^, end walls 35. a base 3 and a cover 31 in the form of a self-closing cover element. For the purpose of opening the box 30, the cover 31 is pivotable about an axis of rotation 33-

As can be seen from the cross-sectional detail in Figure 9. the cover 31 is composed of eleven channels 37 of rectangular cross-section and arranged next to one another. The cross-section of the channels is in this case constant, viewed along the longitudinal direction of the channels. Each channel is filled with a column of liquid 38. The size and/or shape of the cross-section of each channel 37 and the viscosity of the liquid are selected such that as far as possible, and preferably at all times, the liquid remains together as as whole, i.e. as a column.

As will be clear from Figures 9 and 10, the columns of liquid 38 will descend downwards through the channels 37 after the cover 31 is opened, and after the instantaneous line of gravity, which moves during this descent, has passed the perpendicular line through the axis of rotation 33. the cover 31 will move back to the closed position. After the cover 31 has thus fallen back into the closed position, the columns of liquid 38, owing to the sloping position of the cover 31. ⁱⁿ the closed position will move back through the channels 37 in the opposite direction.

Figures 11, 12, and 13 show a further embodiment of the self- closing cover element 42 according to the invention used with a box or container 40. As will be clear, the box or container 40 essentially comprises upright side walls running in the peripheral direction, a base and a self-closing cover 42 according to the invention.

The box or container is suitable, for example, for holding unpackaged foodstuffs, sweets or confectionery. The self-closing cover 42 is rotatable about an axis of rotation 43 or pivot pin 3- Furthermore, the cover 42 is provided with a guide track 44, which is preferably closed with respect to the outside. A body in the form of a ball 46 is accommodated in this guide track 44. This ball 46 can move through the guide track 44, during which movement, as will be clear from Figures 12 and 13, in the open position (see Figure 12) the instantaneous line of

gravity will move past the perpendicular line 4l through the pivot pin 43.

The guide track 44, in its part which is situated at a higher level in the open position, i.e. a section lying above, or at least essentially above, the perpendicular line through the pivot pin, is provided on both sides with strips 9 and 50, which form so-called delay means. As shown in Figure 12, the ball 46 can descend downwards between the strips and 50 in an manner which is somewhat restricted on either side by the strips 49 and 0. By suitably selecting the material properties of the strips 49 and 50, and optionally also suitably selecting the material properties and dimensions of the body 46, the time required for the ball 46 to descend downwards between the strips 49 and 50, the so-called time delay, can be adjusted or set as desired. When the ball 46 has completely passed the strips 49 and 50, the ball 46 will continue to move downwards in an essentially unimpeded manner, at least by comparison with the restricted movement between the strips 49 and 50, and in view of the nature of this particular case will execute a type of free fall. When the ball has reached the bottom of the guide track 44, as depicted by broken lines in Figure 12, the cover 42, owing to the sudden interruption of the unrestricted movement of the ball 46 (in the case of Figure 12, due to the steep position, almost a free-fall motion) will undergo an impact which causes the cover to close.

When the cover has then closed, as illustrated in Figure 13. the ball will roll downwards from the position C depicted by broken lines along the base of the guide track and will be able to pass beneath the strip 49, 50 owing to the sufficient distance provided for this purpose between the strips 9 and the base 5 of the guide track 4 , and will reach lip 53- As indicated by the arrow, the lip 53 will be pressed downwards by the ball 46, so that the ball 46 can reach the position D indicated by broken lines. If the cover is then moved back into the position shown in Figure 12, by raising the cover, for example manually, the lip 53. s indicated in Figure 12 by means of another arrow, will bend through an angle under the effect of the weight of the ball 46 and will direct the ball 46 between the strips 49 and 50, thus ensuring that the ball 46 descends downwards via the strips and 50 and does not fall back past them, while in the closed position it is correctly ensured that the ball 46 can pass quickly below the strips 49 and 50.

The strips 9 and 50 are open towards the base 52 of the guide track 44. This has the advantage that if the cover is closed manually from the position shown in Figure 12 at a time when the ball 46 is still situated between the strips 49 and 50, the ball 46 can fall downwards betwen the strips 49 and 50 in the direction of the base 2 and can roll to the position D shown in Figure 13 by broken lines.

It is advantageous according to the invention if the strips 49 and 50 are designed such that the ball 46 is subject to a different resistance from each of the strips 49 and 50. This prevents the ball 46 from inadvertently becoming jammed between the strips 49 and 50. It will be clear here that it is also conceivable to make do with one strip 9 or 50 made of a material with suitably selected properties and that on the opposite side of the guide track the ball can make contact with a smooth wall of the guide track. The cover element according to the invention can also be used for functions other than that of a cover of a container, such as for example a litter bin. In principle, it is within the essence and scope of the invention also to realize a self-closing barrier. The cover element according to the invention can also be used to cover pictures or texts.